CEREBELLAR RESEARCH: Electrophysiological characteristics of cerebellar cortical elements: By a combined intracellular injection of HRP through recording microelectrodes, we will attempt to identify various cerebellar cortical neurons and describe their electrophysiological activities to understand how the Purkinje cell firing pause is created by climbing fiber inputs. Topographical relationship of cerebellar cortical projection of the Purkinje cells to the cerebellar nuclei will be accomplished more accurately by combined usage of intracellular and extracellular injection of HRP and autoradiographical techniques. The topographical relationship between the projection neurons of the cerebellar nuclei to the thalamic and the brainstem nuclei will be examined. BASAL GANGLIA: The caudate projection neurons will be identified electrophysiologically by antidromic activation and their detailed morphology analyzed by intracellular injection of HRP. Afferent inputs to the projection neurons and the action on their target neurons will be assessed. Intrinsic organization in the caudate nucleus will be analyzed by identifying neuronal elements and interneuronal relationship will be assessed. Basic membrane physiology, e.g., membrane resistance, capacity, firing pattern, spike initiation, accommodation, etc., of the morphologically identified caudate neurons will be studied. BIBLIOGRAPHIC REFERENCES: Kitai. S.T., Kiyohara, T., and Kocsis, J.D. 1976. Electrophysiological properties of nucleus reticularis tegmenti pontis. Exp. Brain Res., 24: 295-309. Kitai, S.T., Sugimori, M., and Kocsis, J.D. 1976. Excitatory nature of dopamine in the nigro-caudate pathway. Exp. Brain Res., 24:351-363.